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Printed Circuit Boards

IP.com Disclosure Number: IPCOM000095064D
Original Publication Date: 1965-Sep-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Huang, SS: AUTHOR [+3]

Abstract

Printed circuits are sometimes formed by etching away unwanted regions of a thin conductive sheet that is mounted on an insulating support. In a typical process, the etchant is applied to selected areas of the conductive sheet, the unwanted material is etched away, and the circuit board is then inspected. The etchants tend to form an imperfect film on the conductive sheet so that small conductive regions remain in the unwanted areas. Sometimes the etchants are dyed and the boards are visually inspected to assure that the etchant film is continuous in the unwanted regions of the conductive sheet. These methods can be improved by apparatus using a light detector, preferably the optical scanner described on page 653 of this number.

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Printed Circuit Boards

Printed circuits are sometimes formed by etching away unwanted regions of a thin conductive sheet that is mounted on an insulating support. In a typical process, the etchant is applied to selected areas of the conductive sheet, the unwanted material is etched away, and the circuit board is then inspected. The etchants tend to form an imperfect film on the conductive sheet so that small conductive regions remain in the unwanted areas. Sometimes the etchants are dyed and the boards are visually inspected to assure that the etchant film is continuous in the unwanted regions of the conductive sheet. These methods can be improved by apparatus using a light detector, preferably the optical scanner described on page 653 of this number.

The voids in the etchant are in part caused by organic oil smears on the conductive sheet. Inorganic oils are frequently used for cleaning the conductive sheets. It has been found that differences between organic oils and inorganic oils can be detected optically using the optical scanner referred to. The output of the light sensor in this application can be used to signal that a board should be recleaned or to control the cleaning process itself.

Some etch baths vary in color as they are depleted. The optical scanner can be arranged to sense light transmitted through the etch bath or reflected from the etch bath and to control the composition of the etch bath in response to the output of the light sensor. Alternatel...